An evaporated fuel leak detecting apparatus detects leak of fuel evaporated from a fuel tank or a canister. JP-A-11-30157 describes a system controlling internal pressure of a fuel tank. If it is determined that there is a leak of evaporated fuel, the system closes a valve disposed between the fuel tank and a canister so as to determine whether the leak of evaporated fuel is generated in the fuel tank or components other than the fuel tank.
The system detects the leak of evaporated fuel when the internal pressure of the fuel tank is stable in the state where an ignition switch of an engine of a vehicle is off. The number of times that the detecting of the leak can be conducted is small if the ignition switch is hardly turned off. Further, the system conducts the detecting of the leak by driving a pump that decompresses the fuel tank after a predetermined time period is elapsed when the ignition switch is turned off, so that the system requires electricity for driving the pump and a soak timer that counts the elapsed time period.